The leakage of shallow gas through the casing cement used in well completion is often a problem in oil and gas wells. Such leakage is generally caused by inherent high pressures in oil and gas wells and can create environmental problems and compromise well safety. This leakage most often occurs because of cracks or other imperfections that occur in the cement that is injected into the well during well completion procedures between the surface and production casings.
Techniques for preventing shallow gas leakage are disclosed in Rusch, David W. et al, “Use of Pressure Activated Sealants to Cure Sources of Casing Pressure”, SPE (Society of Petroleum Engineers) Paper 55996. These techniques use the application of an epoxy sealing technique. One disadvantage in using the technique taught by Rusch et al is that high pressure differentials across the source of leakage are required.
There is disclosed and illustrated a method and apparatus for subterranean thermal conditioning of petroleum in oil wells in Canadian patent application 2,208,197 (Isted) which application was laid open in Canada on or about Dec. 18, 1998. This document teaches the use of an electrical induction technique to provide heat to oil, particularly high viscosity heavy oil and oil containing high proportions of wax. Electrical induction is thought to be a much preferred method to supply heat to oil within a well because of the combustibility of the hydrocarbon products. Further, the benefits of this technique over the previous steam application technique include the fact that the steam used may cause damage to the permeability of the reservoir. This change may adversely affect oil production.
The use of electrical induction by Isted which is disclosed in the above-identified '197 application, however, is not contemplated to be also useful for sealing an annular space between surface and production casing.